I would eliminate the altitude from the equation, because as far as I know this motor has an altitude compensator providing input to the ECU. Run the appropriate setting for the fuel you are running, regardless of elevation. Unless you are willing to bet your motor on the quality of fuel that the pump SAYS it's supposed to be......LOL
true, i have put 1000 miles on mine this way with no DET, but i feel if you can throw a higher compression head on your sled without the need to change octane or fuel map, then you can run a factory leaner setting with the stock head and be fine. elevation does make a difference in compression, not only A/F mixture.